Bergmann's rule

Bergmann's rule is an ecogeographical rule that states that within a broadly distributed taxonomic clade, populations and species of larger size are found in colder environments, and species of smaller size are found in warmer regions. Although originally formulated in terms of species within a genus, it has often been recast in terms of populations within a species. It is also often cast in terms of latitude. It is possible that the rule also applies to some plants, such as Rapicactus.

The rule is named after nineteenth century German biologist Carl Bergmann, who described the pattern in 1847, although he was not the first to notice it. Bergmann's rule is most often applied to mammals and birds which are endotherms, but some researchers have also found evidence for the rule in studies of ectothermic species.[2][3] such as the ant Leptothorax acervorum. While Bergmann's rule appears to hold true for many mammals and birds, there are exceptions.[4][5][6]

Larger-bodied animals tend to conform more closely to Bergmann's rule than smaller-bodied animals, at least up to certain latitudes. This perhaps reflects a reduced ability to avoid stressful environments, such as by burrowing.[7] In addition to being a general pattern across space, Bergmann's rule has been reported in populations over historical and evolutionary time when exposed to varying thermal regimes.[8][9][10] In particular, reversible dwarfing of mammals has been noted during two relatively brief upward excursions in temperature during the Paleogene: the Paleocene-Eocene thermal maximum[11] and the Eocene Thermal Maximum 2.[12]

Bergmann's Rule
Bergmann’s rule is an ecologic principle stating that body mass increases with colder climate. Data demonstrating such a relationship in Swedish moose (Eurasian elk) are shown.[1]

Humans

Human populations near the poles, including the Inuit, Aleut, and Sami people, are on average heavier than populations from mid-latitudes, consistent with Bergmann's rule.[13] They also tend to have shorter limbs and broader trunks, consistent with Allen's rule.[13] According to Marshall T. Newman in 1953, Native American populations are generally consistent with Bergmann's rule although the cold climate and small body size combination of the Eastern Inuit, Canoe Nation, Yuki people, Andes natives and Harrison Lake Lillouet runs contrary to the expectations of Bergmann's rule.[14] Newman contends that Bergmann's rule holds for the populations of Eurasia, but it does not hold for those of sub-Saharan Africa.[14]

Explanations

Northern red fox & southern desert red fox
Bergmann's rule illustrated by red foxes from northern and southern populations

The earliest explanation, given by Bergmann when originally formulating the rule, is that larger animals have a lower surface area to volume ratio than smaller animals, so they radiate less body heat per unit of mass, and therefore stay warmer in cold climates. Warmer climates impose the opposite problem: body heat generated by metabolism needs to be dissipated quickly rather than stored within.[15]

Thus, the higher surface area-to-volume ratio of smaller animals in hot and dry climates facilitates heat loss through the skin and helps cool the body. It is important to note that when analyzing Bergmann's Rule in the field that groups of populations being studied are of different thermal environments, and also have been separated long enough to genetically differentiate in response to these thermal conditions.[15]

In marine crustaceans, it has been proposed that an increase in size with latitude is observed because decreasing temperature results in increased cell size and increased life span, both of which lead to an increase in maximum body size (continued growth throughout life is characteristic of crustaceans).[3] The size trend has been observed in hyperiid and gammarid amphipods, copepods, stomatopods, mysids, and planktonic euphausiids, both in comparisons of related species as well as within widely distributed species.[3] Deep-sea gigantism is observed in some of the same groups, probably for the same reasons.[3]

Hesse's rule

In 1937 German zoologist and ecologist Richard Hesse proposed an extension of Bergmann's rule. Hesse's rule, also known as the heart–weight rule, states that species inhabiting colder climates have a larger heart in relation to body weight than closely related species inhabiting warmer climates.[16]

Criticism

According to a 1986 study, Valerius Geist claimed Bergmann's rule to be false: the correlation with temperature is spurious; instead, Geist found that body size is proportional to the duration of the annual productivity pulse, or food availability per animal during the growing season.[17]

Because many factors can affect body size, there are many critics of Bergmann's Rule. Some believe that latitude itself is a poor predictor of body mass. Examples of other selective factors that may contribute to body mass changes are the size of food items available, effects of body size on success as a predator, effects of body size on vulnerability to predation, and resource availability. For example, if an organism is adapted to tolerate cold temperatures, it may also tolerate periods of food shortage, due to correlation between cold temperature and food scarcity.[5] A larger organism can rely on its greater fat stores to provide the energy needed for survival as well being able to procreate for longer periods.

Resource availability is a major constraint on the overall success of many organisms. Resource scarcity can limit the total number of organisms in a habitat, and over time can also cause organisms to adapt by becoming smaller in body size. Resource availability thus becomes a modifying restraint on Bergmann’s Rule.[18]

Plants

Bergmann's rule cannot generally be applied to plants, above all for latitude.[19] Regarding Cactaceae, the case of Carnegiea gigantea, described as "a botanical Bergmann trend" by Niering, Whittaker, & Lowe,[20] has instead been shown to depend on rainfall, particularly winter precipitation, and not temperature, so Bergmann's rule is not applicable to Carnegiea populations.[21] Members of the genus Rapicactus are larger in cooler environments, as their stem diameter increases with altitude and, above all, latitude. Since Rapicactus grow in a distributional area in which average precipitation tends to diminish at higher latitudes, and their body size is not conditioned by climatic variables, this could suggest a possible Bergmann trend.[22]

See also

Notes

  1. ^ Sand, Håkan K.; Cederlund, Göran R.; Danell, Kjell (June 1995). "Geographical and latitudinal variation in growth patterns and adult body size of Swedish moose (Alces alces)". Oecologia. 102 (4): 433–442. Bibcode:1995Oecol.102..433S. doi:10.1007/BF00341355. PMID 28306886.
  2. ^ Olalla-Tárraga, Miguel Á.; Rodríguez, Miguel Á.; Hawkins, Bradford A. (2006). "Broad-scale patterns of body size in squamate reptiles of Europe and North America". Journal of Biogeography. 33 (5): 781–793. doi:10.1111/j.1365-2699.2006.01435.x.
  3. ^ a b c d Timofeev, S. F. (2001). "Bergmann's Principle and Deep-Water Gigantism in Marine Crustaceans". Biology Bulletin (Russian Version, Izvestiya Akademii Nauk, Seriya Biologicheskaya). 28 (6): 646–650 (Russian version, 764–768). doi:10.1023/A:1012336823275. (Subscription required (help)). Cite uses deprecated parameter |subscription= (help)
  4. ^ Meiri, S.; Dayan, T. (2003-03-20). "On the validity of Bergmann's rule". Journal of Biogeography. 30 (3): 331–351. doi:10.1046/j.1365-2699.2003.00837.x.
  5. ^ a b Ashton, Kyle G.; Tracy, Mark C.; Queiroz, Alan de (October 2000). "Is Bergmann's Rule Valid for Mammals?". The American Naturalist. 156 (4): 390–415. doi:10.1086/303400. JSTOR 10.1086/303400. PMID 29592141.
  6. ^ Millien, Virginie; Lyons, S. Kathleen; Olson, Link; et al. (May 23, 2006). "Ecotypic variation in the context of global climate change: Revisiting the rules". Ecology Letters. 9 (7): 853–869. doi:10.1111/j.1461-0248.2006.00928.x. PMID 16796576.
  7. ^ Freckleton, Robert P.; Harvey, Paul H.; Pagel, Mark (2003). "Bergmann's rule and body size in mammals". The American Naturalist. 161 (5): 821–825. doi:10.1086/374346. JSTOR 10.1086/374346. PMID 12858287.
  8. ^ Smith, Felia A.; Betancourt, Julio L.; Brown, James H. (December 22, 1995). "Evolution of Body Size in the Woodrat over the Past 25,000 Years of Climate Change". Science. 270 (5244): 2012–2014. Bibcode:1995Sci...270.2012S. doi:10.1126/science.270.5244.2012. (Subscription required (help)). Cite uses deprecated parameter |subscription= (help)
  9. ^ Huey, Raymond B.; Gilchrist, George W.; Carlson, Margen L.; Berrigan, David; Serra, Luı́s (January 14, 2000). "Rapid Evolution of a Geographic Cline in Size in an Introduced Fly". Science. 287 (5451): 308–309. Bibcode:2000Sci...287..308H. doi:10.1126/science.287.5451.308. PMID 10634786. (Subscription required (help)). Cite uses deprecated parameter |subscription= (help)
  10. ^ Hunt, Gene; Roy, Kaustuv (January 31, 2006). "Climate change, body size evolution, and Cope's rule in deep-sea ostracodes" (PDF). Proceedings of the National Academy of Sciences of the United States of America. 103 (5): 1347–1352. Bibcode:2006PNAS..103.1347H. doi:10.1073/pnas.0510550103. PMC 1360587. PMID 16432187.
  11. ^ Secord, Ross; Bloch, Jonathan I.; Chester, Stephen G. B.; et al. (February 24, 2012). "Evolution of the Earliest Horses Driven by Climate Change in the Paleocene-Eocene Thermal Maximum". Science. 335 (6071): 959–962. Bibcode:2012Sci...335..959S. doi:10.1126/science.1213859. PMID 22363006. (Subscription required (help)). Cite uses deprecated parameter |subscription= (help)
  12. ^ Erickson, Jim (November 1, 2013). "Global warming led to dwarfism in mammals — twice". University of Michigan. Retrieved 2013-11-12.
  13. ^ a b Holliday, Trenton W.; Hilton, Charles E. (June 2010). "Body proportions of circumpolar peoples as evidenced from skeletal data: Ipiutak and Tigara (Point Hope) versus Kodiak Island Inuit". American Journal of Physical Anthropology. 142 (2): 287–302. doi:10.1002/ajpa.21226. PMID 19927367.
  14. ^ a b Newman, Marshall T. (August 1953). "The Application of Ecological Rules to the Racial Anthropology of the Aboriginal New World". American Anthropologist. 55 (3): 311–327. doi:10.1525/aa.1953.55.3.02a00020.
  15. ^ a b Brown, James H.; Lee, Anthony K. (January 1969). "Bergmann's Rule and Climatic Adaptation in Woodrats (Neotoma)". Evolution. 23 (2): 329–338. doi:10.2307/2406795. JSTOR 2406795.
  16. ^ Baum, Steven (January 20, 1997). "Hesse's rule". Glossary of Oceanography and the Related Geosciences with References. Texas Center for Climate Studies, Texas A&M University. Retrieved 2011-01-09.
  17. ^ Geist, Valerius (April 1987). "Bergmann's rule is invalid". Canadian Journal of Zoology. 65 (4): 1035–1038. doi:10.1139/z87-164.
  18. ^ Clauss, Marcus; Dittmann, Marei T.; Müller, Dennis W. H.; et al. (October 2013). "Bergmann′s rule in mammals: A cross-species interspecific pattern" (PDF). Oikos. 122 (10): 1465–1472. doi:10.1111/j.1600-0706.2013.00463.x.
  19. ^ Moles, Angela T.; Warton, David I.; Warman, Laura; Swenson, Nathan G.; Laffan, Shawn W.; Zanne, Amy E.; Pitman, Andy; Hemmings, Frank A.; Leishman, Michelle R. (2009-09-01). "Global patterns in plant height". Journal of Ecology. 97 (5): 923–932. doi:10.1111/j.1365-2745.2009.01526.x. ISSN 1365-2745.
  20. ^ Niering, W.A., Whittaker, R.H. & Lowe, C.H. (1963). "The saguaro: a population in relation to environment". Science. 142 (3588): 15–23. Bibcode:1963Sci...142...15N. doi:10.1126/science.142.3588.15. PMID 17812501.CS1 maint: Multiple names: authors list (link)
  21. ^ Drezner, Taly Dawn (2003-03-01). "Revisiting Bergmann's rule for saguaros (Carnegiea gigantea (Engelm.) Britt. and Rose): stem diameter patterns over space". Journal of Biogeography. 30 (3): 353–359. doi:10.1046/j.1365-2699.2003.00834.x. ISSN 1365-2699.
  22. ^ Donati, Davide; Bianchi, Claudia; Pezz i, Giovanna; Conte, Lucia; Hofer, Anton; Chiarucci, Alessandro (2016). "Biogeography and ecology of the genus Turbinicarpus (Cactaceae): environmental controls of taxa richness and morphology". Systematics and Biodiversity. 15 (4): 361–371. doi:10.1080/14772000.2016.1251504.

References

Allen's rule

Allen's rule is an ecogeographical rule formulated by Joel Asaph Allen in 1877, broadly stating that animals adapted to cold climates have shorter limbs and body appendages than animals adapted to warm climates. More specifically, it states that the body surface area-to-volume ratio for homeothermic animals varies with the average temperature of the habitat to which they are adapted (i.e. the ratio is low in cold climates and high in hot climates).

Azure kingfisher

The azure kingfisher (Ceyx azureus) is a small kingfisher (17–19 centimetres (6.7–7.5 in)), in the river kingfisher subfamily, Alcedininae. It is found in Northern and Eastern Australia and Tasmania, as well as the lowlands of New Guinea and neighbouring islands, and out to North Maluku and Romang.

It is a very colourful bird, with deep blue to azure back, a large white to buff spot on side of neck and throat, rufous-buff with some blue-violet streaks on breast and flanks. The feet are red with only two forward toes. The lores (the region between the eye and the bill) are white and inconspicuous except in front view, where they stand out as two large white eye-like spots which may have a role in warding off potential predators.

The subspecies differ only in minor details. ruficollaris is smaller, brighter, and has more blue on the flanks. diemenensis is rather large, short-billed, and has a distinctly darker crown. lessoni is more contrasting, with little blue on the flanks. affinis has a red billtip, as has the smaller yamdenae, and ochrogaster is very pale below. Still, there is very little intergradation in the areas where subspecies meet. Comparing subspecific variation with climate data, the former's pattern does not follow and in some instances runs contrary to Bergmann's Rule and Gloger's Rule (Schodde & Mason, 1976, Woodall, 2001).

The contact zone between the mainland Australian subspecies is along the east coast of Far North Queensland, between Cairns and Princess Charlotte Bay (Schodde & Mason 1976), that of the New Guinea ones between Simbu Province and the northern Huon Peninsula, as well as south of Cenderawasih Bay (Woodall, 2001).

Habitat includes the banks of vegetated creeks, lakes, swamps, tidal estuaries and mangroves. Often difficult to see until it quickly darts from a perch above water. Feeds on freshwater yabbies and small fish. Nest in a chamber up to 1 metre long in an earthen creek bank. 5–7 white, rounded, glossy eggs. Voice is a high-pitched, shrill, 'pseet-pseet'.

Bergmann

Bergmann is a surname which is German or Swedish, in origin, respectively. It means "mountain man" in both languages, as well as "miner" in German. Bergman is also a common surname in the Netherlands.

The surname may refer to:

Art Bergmann (born 1953), Canadian rock singer-songwriter

Carl Bergmann (disambiguation), multiple people

Carl Bergmann (anatomist), (1814-1865) German anatomist, physiologist, and biologist who developed the Bergmann's rule.

Daniel Bergmann (born 1962) Czech filmmaker and media mogul, son of Pavel Bergmann.

Erika Bergmann (1915–1996), Nazi guard during World War II

Ernst Bergmann (philosopher) (1881-1945), German philosopher and proponent of Nazism

Ernst David Bergmann (1903-1975), Israeli chemist and founder of nuclear program

Ernst von Bergmann (1836-1907), Baltic German surgeon who introduced principles of aseptic surgery

Gretel Bergmann (1914–2017), Jewish athlete who competed as a high jumper in Germany during the 1930s

Heinrich Bergmann - head of the Criminal Division of the German Kripo in German-occupied Estonia

Hugo Bergmann (1883-1975), German/Israeli Jewish philosopher

Gustav Bergmann (May 4, 1906 - April 21, 1987), Austrian-born American Philosopher

Juliette Bergmann (born 1958), Dutch female bodybuilder

Martin S. Bergmann (1913–2014), psychoanalyst, son of Hugo Bergmann

Michael Bergmann, American filmmaker, grandson of Hugo Bergmann

Pavel Bergmann, (1930-2005) Czech Philosopher & Historian, signatory of Charter 77, nephew of Hugo Bergmann

Peter Bergmann (?-2009) alias used by an unidentified German-speaking man who died under mysterious circumstances

Peter Gabriel Bergmann (1915-2002) German-American physicist

Ralph Bergmann (born 1970), German volleyball player

Sabine Bergmann-Pohl (born 1946), a German conservative politician who served as the last head of state of the German Democratic Republic

Samuel Bergmann, the same as Hugo Bergmann, or Pavel Bergmann's grandson and Hugo Bergmann's great nephew.

Stefan Bergmann (1895-1977) mathematician

Thaisa Storchi Bergmann is a leading Brazilian astrophysicist

Theodor Bergmann (1850-1931), founder of the company Bergmann in Suhl

Walter Bergmann (composer) (1902–1988), German composer and musician

Biological rules

A biological rule or biological law is a generalized law, principle, or rule of thumb formulated to describe patterns observed in living organisms. Biological rules and laws are often developed as succinct, broadly applicable ways to explain complex phenomena or salient observations about the ecology and biogeographical distributions of plant and animal species around the world, though they have been proposed for or extended to all types of organisms. Many of these regularities of ecology and biogeography are named after the biologists who first described them.From the birth of their science, biologists have sought to explain apparent regularities in observational data. In his biology, Aristotle inferred rules governing differences between live-bearing tetrapods (in modern terms, terrestrial placental mammals). Among his rules were that brood size decreases with adult body mass, while lifespan increases with gestation period and with body mass, and fecundity decreases with lifespan. Thus, for example, elephants have smaller and fewer broods than mice, but longer lifespan and gestation. Rules like these concisely organized the sum of knowledge obtained by early scientific measurements of the natural world, and could be used as models to predict future observations. Among the earliest biological rules in modern times are those of Karl Ernst von Baer (from 1828 onwards) on embryonic development, and of Constantin Wilhelm Lambert Gloger on animal pigmentation, in 1833.

There is some scepticism among biogeographers about the usefulness of general rules. For example, J.C. Briggs, in his 1987 book Biogeography and Plate Tectonics, comments that while Willi Hennig's rules on cladistics "have generally been helpful", his progression rule is "suspect".

Carl Bergmann (anatomist)

Carl Georg Lucas Christian Bergmann (18 May 1814 – 30 April 1865) was a German anatomist, physiologist and biologist who developed the Bergmann's rule.

Chronospecies

A chronospecies is a species derived from a sequential development pattern which involves continual and uniform changes from an extinct ancestral form on an evolutionary scale. This sequence of alterations eventually produces a population which is physically, morphologically, and/or genetically distinct from the original ancestors. Throughout this change, there is only one species in the lineage at any point in time, as opposed to cases where divergent evolution produces contemporary species with a common ancestor. The related term paleospecies (or palaeospecies) indicates an extinct species only identified with fossil material. This identification relies on distinct similarities between the earlier fossil specimens and some proposed descendant, although the exact relationship to the later species is not always defined. In particular, the range of variation within all the early fossil specimens does not exceed the observed range which exists in the later species.

A paleosubspecies (or palaeosubspecies) identifies an extinct subspecies which evolved into the currently existing form. This connection with relatively recent variations, usually from the Late Pleistocene, often relies on the additional information available in subfossil material. Most of the current species have changed in size adapting to the climatic changes during the last ice age (see Bergmann's Rule).

The further identification of fossil specimens as part of a "chronospecies" relies on additional similarities which more strongly indicate a specific relationship with a known species. For example, relatively recent specimens – hundreds of thousands to a few million years old – with consistent variations (e.g. always smaller but with the same proportions) as a living species might represent the final step in a chronospecies. This possible identification of the immediate ancestor of the living taxon may also rely on stratigraphic information to establish the age of the specimens.

The concept of chronospecies is related to the phyletic gradualism model of evolution, and also relies on an extensive fossil record, since morphological changes accumulate over time and two very different organisms could be connected by a series of intermediaries.

Cinereus shrew

The cinereous shrew or masked shrew (Sorex cinereus) is a small shrew found in Alaska, Canada and the northern United States. This is the most widely distributed shrew in North America, where it is also known as the common shrew.

Cline (biology)

In biology, a cline (from the Greek “klinein”, meaning “to lean”) is a measurable gradient in a single character (or biological trait) of a species across its geographical range. First coined by Julian Huxley in 1938, the “character” of the cline referred to is usually genetic (e.g allele frequency, blood type), or phenotypic (e.g. body size, skin pigmentation). Clines can show smooth, continuous gradation in a character, or they may show more abrupt changes in the trait from one geographic region to the next.A cline refers to a spatial gradient in a specific, singular trait, rather than a gradient in a population as a whole. A single population can therefore theoretically have as many clines as it has traits. Additionally, Huxley recognised that these multiple independent clines may not act in concordance with each other. For example, it has been observed that in Australia, birds generally become smaller the further towards the north of the country they are found. In contrast, the intensity of their plumage colouration follows a different geographical trajectory, being most vibrant where humidity is highest and becoming less vibrant further into the arid centre of the country.

Because of this, clines were defined by Huxley as being an “auxiliary taxonomic principle”; that is, clinal variation in a species is not awarded taxonomic recognition in the way subspecies or species are.While the terms “ecotype” and “cline” are sometimes used interchangeably, they do in fact differ in that “ecotype” refers to a population which differs from other populations in a number of characters, rather than the single character that varies amongst populations in a cline.

Cold and heat adaptations in humans

Cold and heat adaptations in humans are a part of the broad adaptability of Homo sapiens. Adaptations in humans can be physiological, genetic, or cultural, which allow people to live in a wide variety of climates. There has been a great deal of research done on developmental adjustment, acclimatization, and cultural practices, but less research on genetic adaptations to cold and heat temperatures.

The human body always works to remain in homeostasis. One form of homeostasis is thermoregulation. Body temperature varies in every individual, but the average internal temperature is 37.0 °C (98.6 °F). Stress from extreme external temperature can cause the human body to shut down. Hypothermia can set in when the core temperature drops to 35 °C (95 °F). Hyperthermia can set in when the core body temperature rises above 37.5-38.3 °C (99.5-100.9 °F). These temperatures commonly result in mortality. Humans have adapted to living in climates where hypothermia and hyperthermia are common primarily through culture and technology, such as the use of clothing and shelter.

Deep-sea gigantism

In zoology, deep-sea gigantism, also known as abyssal gigantism, is the tendency for species of invertebrates and other deep-sea dwelling animals to be larger than their shallower-water relatives. Proposed explanations involve adaptation to scarcer food resources, greater pressure or colder temperature at depth.

Gigantothermy

Gigantothermy (sometimes called ectothermic homeothermy or inertial homeothermy) is a phenomenon with significance in biology and paleontology, whereby large, bulky ectothermic animals are more easily able to maintain a constant, relatively high body temperature than smaller animals by virtue of their smaller surface area to volume ratio. A bigger animal has proportionately less of its body close to the outside environment than a smaller animal of otherwise similar shape, and so it gains heat from, or loses heat to, the environment much more slowly.The phenomenon is important in the biology of ectothermic megafauna, such as large turtles, and aquatic reptiles like ichthyosaurs and mosasaurs. Gigantotherms, though almost always ectothermic, generally have a body temperature similar to that of endotherms. It has been suggested that the larger dinosaurs would have been gigantothermic, rendering them virtually homeothermic.

Leptothorax acervorum

Leptothorax acervorum is a small brown to yellow ant in the subfamily Myrmicinae. It was first described by Johan Christian Fabricius in 1793. L. acervorum is vastly distributed across the globe, most commonly found in the coniferous forests of Central, Western and Northern Europe. The morphology of L. acervorum is extremely similar to that of other Leptothorax ants. The difference arises in the two-toned appearance of L. acervorum, with the head and metasoma being darker than the mesosoma segment of the body, and hair across its body. Following Bergmann's rule—unusually, for ectothermic animals—body size increases with latitude.

Mancallinae

The Mancallinae were a group of prehistoric flightless auk relatives that lived on the Pacific coast of today's California and Mexico from the late Miocene epoch to the early Pleistocene (ranging from at least 7.4 million to 470,000 years ago). They are sometimes collectively referred to as Lucas auks after the scientist who described the first species, Frederic Augustus Lucas.

They had evolved along somewhat similar lines as the great auk, their North Atlantic ecological counterpart, but their decidedly stubbier wings were in some aspects more convergent with penguins.

Compared with the subarctic great auk, they were also smaller (see also: Bergmann's Rule): Praemancalla species have been estimated to have weighed about 3 kg. Most Mancalla forms weighed somewhat less (about 2.4 kg), with M. milleri being a smaller (1.65 kg) and M. emlongi a much larger bird (3.8 kg) than the rest. The last species thus stood around 55–60 cm high in life. The largest species, Miomancalla howardi, was the largest charadriiforme of all time.

Megafauna

In terrestrial zoology, megafauna (from Greek μέγας megas "large" and New Latin fauna "animal life") are large or giant animals. The most common thresholds used are weight over 40 kilograms (90 lb) or 44 kilograms (100 lb) (i.e., comparable or larger in mass than a human) or over a tonne, 1,000 kilograms (2,205 lb) (i.e., comparable or larger in mass than an ox). The first of these include many species not popularly thought of as overly large, such as white-tailed deer and red kangaroo.

In practice, the most common usage encountered in academic and popular writing describes land mammals roughly larger than a human that are not (solely) domesticated. The term is especially associated with the Pleistocene megafauna – the land animals often larger than modern counterparts considered archetypical of the last ice age, such as mammoths, the majority of which in northern Eurasia, the Americas and Australia became extinct within the last forty thousand years. It is also commonly used for the largest extant wild land animals, especially elephants, giraffes, hippopotamuses, rhinoceroses, and large bovines. (Of these five categories of large herbivorous mammals, only bovines are presently found outside of Africa and southern Asia, but all the others were formerly more wide-ranging.) Megafaunal species may be subcategorized by their trophic position into megaherbivores (e.g., elephants), megacarnivores (e.g., lions), and, more rarely, megaomnivores (e.g., bears).

Other common uses are for giant aquatic species, especially whales, any larger wild or domesticated land animals such as larger antelope and cattle, as well as numerous dinosaurs and other extinct giant reptilians.

The term is also sometimes applied to animals (usually extinct) of great size relative to a more common or surviving type of the animal, for example the 1 m (3 ft) dragonflies of the Carboniferous period.

Pack rat

A pack rat or packrat, also called a woodrat, can be any of the species in the rodent genus Neotoma. Pack rats have a rat-like appearance with long tails, large ears and large black eyes. Compared to deer mice, harvest mice and grasshopper mice, pack rats are noticeably larger and are usually somewhat larger than cotton rats.

Penguin

Penguins (order Sphenisciformes, family Spheniscidae) are a group of aquatic flightless birds. They live almost exclusively in the Southern Hemisphere, with only one species, the Galapagos penguin, found north of the equator. Highly adapted for life in the water, penguins have countershaded dark and white plumage, and their wings have evolved into flippers. Most penguins feed on krill, fish, squid and other forms of sea life which they catch while swimming underwater. They spend roughly half of their lives on land and the other half in the sea.

Although almost all penguin species are native to the Southern Hemisphere, they are not found only in cold climates, such as Antarctica. In fact, only a few species of penguin live so far south. Several species are found in the temperate zone, and one species, the Galápagos penguin, lives near the equator.

The largest living species is the emperor penguin (Aptenodytes forsteri): on average, adults are about 1.1 m (3 ft 7 in) tall and weigh 35 kg (77 lb). The smallest penguin species is the little blue penguin (Eudyptula minor), also known as the fairy penguin, which stands around 40 cm (16 in) tall and weighs 1 kg (2.2 lb). Among extant penguins, larger penguins inhabit colder regions, while smaller penguins are generally found in temperate or even tropical climates (see also Bergmann's rule). Some prehistoric species attained enormous sizes, becoming as tall or as heavy as an adult human. These were not restricted to Antarctic regions; on the contrary, subantarctic regions harboured high diversity, and at least one giant penguin occurred in a region around 2,000 km south of the equator 35 mya, in a climate decidedly warmer than today.

Pleistocene coyote

The Pleistocene coyote (Canis latrans orcutti), also known as the Ice Age coyote, is an extinct subspecies of coyote that lived in western North America during the Late Pleistocene era. Most remains of the subspecies were found in southern California, though at least one was discovered in Idaho. It was part of a carnivore guild that included other canids like foxes, gray wolves, and dire wolves.Compared to their modern Holocene counterparts, Pleistocene coyotes were larger and more robust, weighing 39–46 lb (18–21 kg), likely in response to larger competitors and prey rather than Bergmann's rule. Their skulls and jaws were significantly thicker and deeper than in modern coyotes, with a shorter and broader rostrum and wider carnassial (denoting the large upper premolar and lower molar teeth of a carnivore, adapted for shearing flesh) teeth. These adaptions allowed it to cope with higher levels of stress, when it killed larger prey, compared to modern coyotes. Pleistocene coyotes were also likely more specialized carnivores than their descendants, as their teeth were more adapted to shearing meat, showing fewer grinding surfaces which were better suited for processing vegetation. The lower jaw was also deeper, and the molars showed more signs of wear and breakage than modern populations, thus indicating that the animals consumed more bone than today. Behaviorally, it is likely to have been more social than the modern coyote, as its remains are the third most common in the La Brea Tar Pits, after dire wolves and sabre-toothed cats, both thought to be gregarious species.Their reduction in size occurred within 1,000 years of the occurrence of the Quaternary extinction event, when the climate changed and the majority of their larger prey became extinct. Furthermore, Pleistocene coyotes were unable to successfully exploit the big game hunting niche left vacant after the extinction of the dire wolf, as that gap was rapidly filled by gray wolves. These gray wolves are likely to have actively killed off the larger-bodied coyotes, with natural selection favoring the modern gracile morph. Human predation on the Pleistocene coyote's dwindling prey base may have also impacted the animal's change in morphology.

Surface-area-to-volume ratio

The surface-area-to-volume ratio, also called the surface-to-volume ratio and variously denoted sa/vol or SA:V, is the amount of surface area per unit volume of an object or collection of objects.

In chemical reactions involving a solid material, the surface area to volume ratio is an important factor for the reactivity, that is, the rate at which the chemical reaction will proceed.

For a given volume, the object with the smallest surface area (and therefore with the smallest SA:V) is the sphere, a consequence of the isoperimetric inequality in 3 dimensions. By contrast, objects with tiny spikes will have very large surface area for a given volume.

Temperature-size rule

The temperature-size rule denotes the plastic response (i.e. phenotypic plasticity) of organismal body size to environmental temperature variation .Organisms exhibiting a plastic response are capable of allowing their body size to fluctuate with environmental temperature. First coined by David Atkinson in 1996, it is considered to be a unique case of Bergmann's rule that has been observed in plants, animals, birds, and a wide variety of ectotherms . Although exceptions to the temperature-size rule exist, recognition of this widespread "rule" has amassed efforts to understand the physiological mechanisms (via possible tradeoffs) underlying growth and body size variation in differing environmental temperatures .

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